Snap acting condition responsive device



Patented Dec. 23, 1941 2,267,104 SNAP ACTING CONDITION RESPONSIVE DEVICE Alwin B. Newton, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application September 30, 1939, Serial No. 297,290

19 Claims.

The present invention relates to a condition responsive device and more particularly to one designed to operate with a snap action.

In many instances, in the condition controlling art, it is desirable to have a condition responsive device which upon the condition reaching a predetermined value, operates switch contacts or other control members with a snap action. Such a snap movement is essential in the case of switches in order to reduce arcing between the contact points. There are many other cases in which a snap movement may be desirable. Thus, in the gas burning art it is often desirable to move the gas valve with a snap action to prevent pop back in the burner mixing chamber. The present invention is concerned with an improved form 01' condition responsive snap action device characterized by an extremely simple construction.

An object of the present invention is to provide a snap acting condition responsive device comprising a channel shaped member of resilient material and a second member secured to such channel shaped member at longitudinally spaced points thereof, said members having different rates of expansion and contraction with change in the value of the condition whereby upon the condition reaching a predetermined-value, the channel shaped member is abruptly bent.

A further object of the present invention is to provide such a device in which switch contacts are actuated thereby.

A still further object of the present invention is to provide such a condition responsive arrangement in which one of the members is responsive to one condition and the other member to a second condition so that the device as a whole is responsive to the resultant of the two conditions.

A still further object of the present invention is to provide such an arrangement in which the condition is a temperature condition.

A further object of the present invention is to provide such a device in which the condition is effective temperature.

A stlil further object of the device is to provide such an arrangement in which the device responds to the wet bulb temperature.

An even further object of the device is to provide such an arrangement in which the device responds to the amount of wet bulb depression.

Other objects of the present invention will be apparent from a consideration of the accompanying specification, claims and drawing, in which the condition responsive device oi the present invention;

Figure 2 is a side elevational view of the device employed as a thermostatic switch;

Figure 3 is a view of the device of Figure 2 in its contact making position;

Figure 4 is a plan view of the device adapted for the control of humidity;

Figure 5 is an end elevational view of the device of Figure 4;

Figure 6 is a plan view of a modification of the device adapted to respond to eflfective temperature;

Figure 7 is a plan view of a modification of the device adapted to respond to wet bulb temperature, and

Figure 8 is a modification of the device adapted to respond to wet bulb depression.

Referring to Figure 1, the device as illustrated therein comprises a lower channel shaped member ID and an upper channel shaped member H. The lower channel shaped member is made of resilient material, preferably a resilient metal, and comprises a base portion 12 and flanges I3 and It. The upper channel shaped member H is formed of somewhat heavier material so as to constitute a relatively rigid member. The upper member ll similarly comprises a base portion l5 and two flanges l6 and I1. The base portion I! of member ID is cut away for a substantial portion of its length as indicated at IS, the width of the cut-away portion being slightly greater than the width of member H. The flanges l6 and ll of member ll extend only over the length of this cut-away portion I9. The portions of base l5 of member H that project beyond the flanges l6 and H are secured to the base of member ID by welding or in some other similar manner. The flanges l6 and ll of the upper member I l are perpendicular to the base so as to make member ll relativelyrigid. The flanges l3 and ll of the lower member Hl, however, are disposed at an obtuse angle with respect to the base so that they do not resist bending to as great an extent as if they were perpendicular to the base. understood that the expression channel shaped as used in the specification and claims is intended to refer to any member having at least two portions disposed angularly with respect to each other along a longitudinal axis to provide a channel or trough.

The device as shown in Figure 1 is intended to respond to dry bulb temperature. Either member Ill or member ll may be made responsive to Figure 1 is a perspective view of one form of temperature by being formed of material having Itistobe a relatively high temperature coeflicient of expansion. The other member is preferably made of material substantially unaffected by temperature changes. If it is desired, however, both members In and II may be made effective to temperature but to different degrees. In any of the above cases, changes in temperature will result in one of the members changing in length with respect to the other. In Figures 2 and 3, the device is shown as applied to a switch and the operation is shown in the case in which the upper member H becomes shorter than the lower member In. It will be noted that the right-hand end of members l and II are rigidly mounted in a block 2|. The left-hand end of base portion l5 of member It carries a contact 22 which is adapted to be engaged with a contact 23 carried by a suitable support 24. Let itbe assumed that member II has the highest temperature coefilcient of expansion and member ill the lower coefficient of expansion. As the elements are shown in Figure 2, the members Ill and II are substantially the same in length so that the channel shaped member l0 assumes normal channel shape. If the temperature begins to drop, member II will tend to shorten in length with respect to member I 0 tending to bow the ends of member ID upwardly. This tendency is resisted by the fact that the flanges l3 and I4 do not lie in the same plane and therefore resist bending transversely of the member I0. The result is that the bending stress is gradually increased without any bending of member ID until the bending stress reaches a predetermined value at which the middle portions of flanges l3 and I 4 are abruptly forced into a position in which they lie in the same straight line. Member I0 is then able to bend freely about its mid portion. This action is clearly illustrated in Figure 3 wherein member ID is bent around a point generally designated by the reference numeral 26. It will be noted that member II is still perfectly straight, the only bending thereof being in the extending portions of the base portion l5. As indicated in Figure 3, the bending of channel shaped member ID upwardly moves contacts 22 and 23 into engagement. This engagement, moreover, is effected with a snap action.

When the temperature begins to rise, the channel shaped member II will lengthen with respect to member l0. As the length of this member tends to approach that of member ill, the resiliency of the side portions l3 and M will subsequently cause channel shaped member Hi to assume its original form thereby abruptly moving contacts 22 and 23 out of engagement. It will thus be seen that with the extremely simple construction of the present arrangement, a very decisive'snap movement in both directions is provided.

While the condition has been discussed in which member I I shortens with respect to member I0, the device will also work to provide snap action in the other direction when member ll becomes longer than member l0. Any tendency of member H to become longer than member I 0 applies a bending stress to member ID tending to move the outer ends thereof downwardly with respect to the central portion. This is likewise resisted by the flanges i3 and I4 until the stress reaches a predetermined value, at which the outer ends will be bent downwardly in an abrupt movement. The'cut-away portion IQ of base l2 of member ID permits this movement since in order for this movement to take place the mid portion forms a chord of this are as clearly indicated in Figure 3. Where the bending is in the other direction, a portion of this chord must lie below the upper surface of base l2. The opening l9 makes this possible. The device thuscan, if desired, be utilized to provide a three position switch which moves between each of its positions with a snap action. Thus in the case in which member II is the more highly expansible, when the temperature drops sufiiciently member I0 is snapped from the position shown in Figure 2 to that shown in Figure 3. When the temperature rises considerably above the value corresponding to the position of Figure 2, member I0 is snapped downwardly away from the position shown in Figure 2. If desired, an extra contact may be provided on the under side of member ID to engage with a fixed contact beneath the device.

In Figure 4, there is shown a modification in which the device is responsive to relative humidity. In this species as in all of the species there is a lower channel shaped member which is designated in this species by the reference numeral 30. It is to be understood that this member corresponds as far as structural details is concerned to member 10. In other words, this member has side flanges 3| and 32 which are bent downwardly to resist transverse bending of member 30. In the present species the other element of the unit is formed of a humidity responsive element. Any type of element may be used which has the property of expanding and contracting with changes in humidity. In the present case the humidity responsive unit comprises a number of silk strands 33 which are secured at their ends between the member 30 and bars 35 and 36. As indicated in Figure 5, these bars are securely fastened by rivets 39 or other suitable fastening means to the member 36 and thus serve to securely clamp the ends of strands 33. Silk is one of a number of materials which has the property of contracting upon increase in relative humidity. The clamping bar 35 carries a contact 38 corresponding to the contact 22.

The element is shown in Figures 4 and 5 in the position it assumes when the length of the humidity responsive strands 33 is approximately the same as that of member 30. It is to be understood that member 30 is relatively insensitive both to changes in temperature and humidity. This member may, for example, be made of Invar or some similar material. Thus as the humidity increases, a point will be reached at which suitable tension is applied to member 30 tending to bend the ends of the same into the position shown in Figure 3 in connection with that species. As in the case of the previous species, this bending is initially resisted by side flanges 3| and 32 which ultimately abruptly yield to permit such bending and hence to permit abrupt movement of contact 38 into engagement with its cooperating contact (not shown). When the temperature rises again, the length of the strands 33 will eventually permit the member 30 to abruptly assume its original form causing separation of contact 38 from its associated contact. The device of Figures 4 and 5 thus provides an extremely simple device for controlling humidifying apparatus in accordance with the value of the relative humidity.

In Figure 6, there is shown a device which may be employed for control in accordance with effective temperature. The device is structurally similar to that of Figures 4 and 5 comprising a channel shaped base member 40 and silk strands 43 clamped between end members 45 and 46. The only difierence between the devices of the two figures is that in the species of Figures 4 and 5, member is unafiected by temperature change whereas in the species of Figure 6 member has a substantial temperature coefiicient of expansion as indicated by the legends adjacent these figures. The result is that an increase in humidity with its accompanying shortening of strands 43 will have no efiect it it is accompanied by a simultaneous and corresponding decrease in the temperature adjacent the device. In such a case the member 40 will shorten as the strands 43 shorten. Under such circumstances, it is not desired to have the device 40 changed since the efiective temperature is remaining constant. If either the humidity alone should increase or if the temperature alone should increase, the strands 43 will become shorter with respect to member 40 so that member 40 is caused to snap into the position corresponding to the position of member III of Figure 3. Secured to clamping bar 45 is a contact 48 which when the member 40 is bent in the manner just described will be moved into engagement with an associated contact (not shown) It will be seen that the device of Figure 6 in value of effective temperature to which it is subjected.

In Figure 7, a modification of the device is shown, this modification being designed to respond to wet bulb temperature. The distortable channel shaped member in this species is designated by the reference numeral 50. As in the other forms, this member comprises a base portion 5i and side flanges 52 and 53. Likewise, as in the other species, the base portion 5! is cut away at 54. Extending between the two remaining portions of base 5| is a relatively rigid metallic strip 55, this strip being formed of material having a relatively high temperature coefiicient of expansion. Member 50 is formed of Invar or some other metal having substantially zero temperature coefiicient of expansion. Surrounding the member is a wick 55, the lower end of which extends into a container 51 containing water. The water will be drawn from the container 51 up through the wick so as to maintain the entire wick saturated. By reason of the presence of wick 55, the metallic strip 55 will be subjected to wet bulb temperature. It is believed that the operation of the device 51 will be obvious in view of the description of the operation of the preceding species. When the wet bulb temperature decreases to a predetermined value, member 50 will be snapped abruptly into the position corresponding to that of Figure 3. This bending movement of member 50 is utilized to actuate a contact 58.

In Figure 8, a still further species of the device is shown. This species is similar to the species of Figure 7 comprising a channel shaped member having a cut-away base portion 5|, the two parts of which are bridged by a strip having a substantial temperature coeflicient'of expansion. A wick 55 surrounds this member 55 and the lower end of the wick extends into a suitable container of water to keep the same saturated as in the species of Figure 7. The member 55 similarly carries a contact 68 designed to be moved upon the bending of member 60. As indicated by the legends on the drawing, the essential difference between the species of Figures 7 and 8 is that member 60 is responsive to temperature changes while member 50 is not. The two members 55 and 60 are made of materials having substantially the same temperature coeflicients of expansion so that the bending force exerted by member '50 is a function of the difierence between wet and dry bulb temperatures. In other words, member 55 is responsive to dry bulb temperature. When the difference between these two temperatures reaches a predetermined value, member 50 is abruptly bent with a snap action to cause actuation of contact 68.

While various specific embodiments of the invention have been disclosed for purposes of illustration, it is to be understood that the invention is limited only by the scope of the appended claims.

I claim as my invention: 1. In a condition responsive device, a generally rectangular channel shaped member of resilient material and a second member secured substantially parallel with said channel shaped member at longitudinally spaced points thereof, said members having different rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value said channel shaped member will be abruptly bent.

2. In a condition responsive device, a generally rectangular channel shaped member of resilient material and a second member secured substantially parallel with the convex side of said channel shaped member at longitudinally spaced points thereof, said members having different rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value said channel shaped member will be abruptly bent.

3. In a condition responsive switch, a condition responsive unit comprising a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, said members having difierent rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value said channel shaped member will be abruptly bent, a fixed contact, a movable contact associated with one end of said unit in proximity to said fixed contact, and means for rigidly supporting the other end of said unit.

4. In a condition responsive device, a generally rectangular channel shaped member of resilient material and a relatively rigid second member secured parallel with said channel shaped member at longitudinally spaced points thereof, said members having difierent rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value, said channel shaped member will be abruptly bent.

5. In a temperature responsive device, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, said members having different temperature coeflicients of expansion whereby upon said temperature reaching a predetermined value, said channel shaped member will be abruptly bent.

6. In a condition responsive device, a generally rectangular channel shaped member of resilient material expansive and contractive with changes in the value of a first condition and substantially unafiected by a second condition, a second member secured parallel with said channel shaped member at spaced points thereof, said second member being expansive and contractive with changes in the value of said second condition and substantially unaffected by said first condition whereby upon the values of said tw conditions attaining a predetermined relatio said channel shaped member will be abruptly bent.

'7. In a humidity responsive device, a generally rectangular channel material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, said members having difi'erent rates of expansion and contraction with change in the value of the humidity whereby upon the humidity reaching a predetermined value said channel shaped member will be abrupt- 1y bent.

8. In an effective temperature responsive device, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, one of said members having an appreciable temperature coeflicient of expansion but being relatively unaffected by changes in the value of the humidity, and said other member having the property of expansion and contraction with changes in humidity and being relatively unaffected by changes in temperature, whereby upon the effective temperature assuming a predetermined value said channel shaped member will be abruptly bent.

9. In a wet bulb temperature responsive device, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, one of said members being substantially unaffected by temperature and the other of said members having a relatively large temperature coefiicient of expansion and having a moist body adjacent it, whereby upon the wet bulb temperature reaching a predetermined value said chan-,

nel shaped member will be abruptly bent,

10. In 'a device responsive to the amount of wet bulb depression, a pair of parallelly secured together members each having the same temperature coeificient of expansion, a moist body adjacent one of said members, and means snap actuated in accordance with the relative length of said members.

11. In a device responsive to the amount of wet bulb depression, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, each of said members having the same temperature coefiicient of expansion, and a moist body adjacent one of said members, said members eoacting to cause said channel shaped member to be abruptly bent when the wet bulb depression assumes a predetermined value.

12. In a condition responsive device, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, the sides shaped member of resilient an obtuse angle with respect of said channel shaped member being disposed non-perpendicularly to the base thereof and said members having different rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value the sides of the channel shaped member will be abruptly distorted to permit bending of said channel shaped member.

13. In a condition responsive device, a generally rectangular channel shaped member of resilient material and a second member secured parallel with said channel shaped member at longitudinally spaced points thereof, the sides of said channel shaped member being disposed at to the base thereof and 'said members having different rates of expansion and contraction with change in the value of the condition whereby upon said condition reaching a predetermined value the sides of the channel shaped member will be abruptly distorted to permit bendi g of said channel shaped member.

14. In a condition responsive device, a pair of generally rectangular channel shaped members parallelly disposed back to back and secured together adjacent their ends, the sides of a first of said channel shaped members being disposed perpendicularly to the base thereof and the sides of the other of said channel shaped members being disposed non-perpendicularly to the base thereof, and said members having different rates of expansion and contraction with change in the value ofthe condition whereby upon said condition reaching a predetermined value the sides of said other channel shaped member will be abruptly distorted to permit bending of said member.

15. In a condition responsive device, a resilient generally rectangular member having side flanges which normally lie in intersecting planes, and a second member secured to said resilient member at the ends thereof, said members having difierent form changing characteristics for change in the value of a, variable condition whereby upon said condition reaching a predetermined value a portion of at least one of said fianges will be caused to change in shape and lie in a different plane.

16. A snap acting device comprising a first generally rectangular frame member having a pair of opposite sides disposed in intersecting planes and a second member secured to said first member at the ends thereof, said members having different condition responsive characteristics so that upon said condition reaching a predetermined value a portion of at least one of said sides will be caused to change in shape and lie in a different plane.

17. In a condition responsive device, a first generally rectangular resilient channel shaped member for storing a force, and a force exerting second member parallel with the channel and secured to said first member at the ends thereof, said first and second members having different form changing characteristics for change in the value of the condition whereby upon said condition reaching a predetermined value said first member will change its channel shape and be abruptly bent. I

18. In a condition responsive device, an oblong resilient member having downturned flanges along the longitudinal sides thereof and bridging lateral end pieces at the ends thereof, and a second member secured to said lateral end pieces of said oblong member, said members having different coefiicients of expansionfor change in the value of a variable condition whereby upon said condition reaching a predetermined value said flanges will be caused to change shape to cause said device to move with a snap action.

19. In a condition responsive device, a resilient member formed as a rectangular frame normally lying in a plane, resilient flanges formed as opposite sides of said frame, said flanges normally lying in diflerent planes which intersect the plane of said frame, and a second member secured to opposite ends of said frame, said members having different coefllcients of expansion for change in the value of a variable condition whereby upon said condition reaching a predetermined value said flanges will be caused to change shape to cause said device to move with a snap action.

ALW'IN B. NEWTON. 

